Generally, seatback spring elements for automobiles are arrayed so that they form a flat plane and are firmly secured to or linked via an elastic or resilient means with a seatback frame at the upper and lower ends thereof.
Conventional seatback spring devices for automobiles which include, for example, S-shaped (or wave-like) spring elements will be described with reference to FIGS. 7 to 9.
FIG. 7 is a perspective view showing a prior art device. Headrest frames 2, 2 are secured to both edges of the upper end of a seatback frame 1. A headrest 3 is provided between the headrest frames 2, 2. Lumbar support mechanisms 4 are secured to both sides of the seatback frame 1. Four S-shaped springs 13, 14, 15 and 16 are secured to the upper end of the seatback frame 1 by a bracket 5. The lower ends of the S-shaped spring elements are linked with a torsion spring 10. The torsion spring 10 abuts the lower end of the seatback frame 1.
FIG. 8 is a sectional view taken along the line A--A in FIG. 7 showing the linkages among the bracket 5, S-shaped springs, the torsion spring 3, 11 and the seatback frame 1 in which the horizontal sections are exaggeratedly illustrated. The central area of the S-shaped spring elements are flexed rearwardly by a pressure exerted by a human body and a compression force is applied to the torsion spring 10. Forward and rearward vibrations are absorbed by the S-shaped springs and the torsion spring 10.
FIG. 9 is a sectional view of a horizontal section of each S-shaped spring taken along the line B--B in FIG. 7 illustrating the positional relation between the back of the human body and the S-shaped springs. The S-shaped spring elements are disposed on a common plane.
In the prior art, the body of the occupant is held and the swings and vibrations during running are damped by such a seatback spring device.
However the central area of the seatback spring device is flexed to a greater extent while the flexure at the upper and lower ends is a small amount, since the upper and lower ends of the seatback spring device for automobiles are linked with the seatback frame.
Accordingly, the plane defined by the seatback spring elements which have been elastically deformed during holding a human body will not abut the back of human body at an uniform pressure over an entire surface thereof, so that a gap is inevitably formed therebetween.
Furthermore, it is more difficult for the seatback spring elements defining a flat plane before being applied with a body pressure, to uniformly abut to the back of a human body comprising a complicated surface configuration, since the back of the human body forms a complicated contour during running. A recessed area is formed inwardly at the waist in view of the physique structure and a large gap is formed between the seatback spring device and the waist of human body.
On the other hand, the body pressure is distributed in such a manner that the pressure at the waist (or lumbar) is high based on ergonomics.
However the load applied to the waist by a human body is high since a gap is formed between the waist and the seatback spring and the waist is not secured, and thus the vibrations are not effectively absorbed in accordance with the prior art.
Accordingly, there have been problems in that the fatigue is increased and the running feeling becomes worse.
Besides, there is another problem in that it is difficult to damp the lateral swings and vibrations since the spring elements are arrayed on a flat plane, although the forward and rearward vibrations may be damped. During running and turning, lateral vibrations (or swings) or pressures of the human body are added. Lateral vibrations are generated due to the uneven surface of road, including recesses and protrusions, transmitted to the human body even during running on a straight road.
Since no mechanism for damping lateral vibrations has been provided in the seatback spring in the prior art, a burden is imposed on the human body to induce fatigue and a comfortable feeling can not be obtained. Increased fatigue due to long distance driving and driving on a rough road induces the running feeling, and, additionally, scattering of attention and lack of concentration.
If the seatback spring elements were linked with the seatback frame at lateral ends thereof, it might be possible to damp the lateral vibrations since the seatback spring elements flex in an arcuate manner due to body pressure. However, spaces at both sides of the seatback frame as shown in FIG. 7 are required for installation of adjustment devices for a lumbar support mechanism, a side support mechanism, and a reclining mechanism or the like. Mountings for the seatback frame and mountings for the adjustment devices would have to be provided in the same space. Accordingly, it would become difficult or impossible to mount such adjustment devices. In some cases, alteration of sizes, etc. of the other members might be needed for mounting of such adjustment devices. Furthermore, it would become difficult to eliminate fatigue since the back of the human body can not uniformly be rested by the seatback springs by means of the adjustment devices.
Accordingly, in the prior art of the seatback spring devices for automobiles, there has not been any effective means for allowing the seatback spring elements to suitably abut the back of human body for absorbing the lateral vibrations (or swings) without changing the design of other members.